This application claims the benefit of German patent application 10061546.5, filed Dec. 11, 2000, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a cooling system for an internal combustion engine, such as for a motor vehicle, which is cooled by means of a liquid coolant. The cooling system of the present invention generally includes a coolant pump, a coolant radiator, coolant conduits in a cylinder head, coolant channels in a cylinder block, and a regulating device, which permits the cylinder head and the cylinder block to have different temperatures based upon regulation of the coolant flow.
2. Background of the Invention
Cooling systems of the type described above are known as dual-circuit cooling systems. One such cooling system is described in German patent no. DE 34 40 504 C2. The purpose of a dual-circuit cooling system is to permit the cylinder head and the intake ports to have a different temperature from that of the cylinder block. More than half of the frictional resistance of an internal combustion engine normally occurs in the cylinder block, and it is desirable to increase the efficiency of the engine by reducing frictional resistance. One means of reducing that frictional resistance is to increase the operating temperature of the cylinder block by controlling the coolant flow.
Typically, the cylinder head does not bear the same degree of frictional resistance as the cylinder block. Some beneficial reduction in friction in the cylinder head does occur with a higher operating temperature, specifically with a higher oil temperature, but there are other attendant problems with a higher temperature in the cylinder head and intake ports. For instance, the fill level of the cylinder (the degree to which air for the combustion process is introduced into the cylinder) drops when the cylinder head and intake ports are at a higher temperature. Because less oxygen is present for combustion purposes, the efficiency of the combustion reaction is reduced, wiping out any gains in efficiency that might have been had through reduction of frictional resistance in the cylinder head.
Consequently, it is desirable to achieve an operating condition of the engine such that the cylinder head has a temperature that is, overall, lower than a maximum safe operating temperature and, specifically, lower than that of the cylinder block. The usual solution to this design challenge is to provide a pair of coolant circuits, each of which is provided with its own coolant pump. The coolant circuits can be connected with each other in different ways by means of a valve control group. During warm-up, the two coolant circuits are switched in series, wherein the coolant radiator is bypassed by means of a short-circuit. Once the desired temperature of the cylinder head has been reached, the radiator is connected to the cylinder head coolant circuit, while the cylinder block coolant circuit remains short-circuited across the radiator. Then, when both coolant circuits are at their desired operating temperatures, a portion of the coolant from the cylinder head coolant circuit is admixed with coolant from the cylinder block coolant circuit, which has passed through the radiator. Additionally, temperature sensors are provided in the two coolant circuits in order to signal an electric drive motor of a blower for the coolant radiator to be switched on.
As can be seen from the above description, the design and operation of prior-art dual circuit cooling systems can be complex. Such complexity leads to increased design and manufacturing costs, as well as to an increased likelihood of failure in operation.
It is accordingly an object of the present invention to improve upon, by simplification, prior art dual-circuit cooling systems as described above, and specifically to provide for a unified dual-temperature cooling system that includes a single coolant pump.
In order to meet this object, individual thermostatic valves are connected downstream of the cylinder head and the cylinder block, which valves operate to regulate the flow of coolant individually through the cylinder head and cylinder block based upon the temperature of the coolant flowing through the valves. For instance, when the coolant flowing through the cylinder head to one of the valves is below a predetermined temperature, the valve remains closed and no coolant (or only a trickle flow of coolant) is allowed to be drained from the cylinder head and replaced by cooler-temperature coolant. Likewise, coolant flowing through the cylinder block to the other valve is blocked until the coolant is at a separately determined temperature. In this manner, coolant flowing from a single coolant pump through the cylinder head or the cylinder block is individually regulated. By selecting the opening temperature for the cylinder head valve at a lower temperature than that at which the cylinder block valve is set, the effect of a dual-circuit cooling system is achieved more simply.
Moreover, the two thermostatic valves may have different flow cross-sections, so that when both valves are in their fully opened states, different amounts of coolant flow through one the individual valves and their corresponding engine members. In particular, a lower operating temperature for the cylinder head than for the cylinder block may be achieved, even when both valves are fully open, if the flow cross-section of the cylinder head valve is greater than that of the cylinder block valve. Consequently, more coolant flows through the cylinder head than flows through the cylinder block.
Further features and advantages of the invention are apparent from the claims and the following description of preferred embodiments of the invention in conjunction with the drawings.